The invention relates generally to the purification of chlorofluorocarbons. Such materials are frequently made by the reaction of hydrofluoric acid with chlorinated hydrocarbons so that the chlorine atoms are replaced with fluorine atoms. This process inherently produces byproduct hydrochloric acid while some hydrofluoric acid is left unreacted. Consequently, the fluorinated product must be purified. Typically, this has been done by distillation or similar steps. However, these are expensive and complex and simpler procedures are desirable. In addition, losses of the fluorinated product result.
Several U.S. patents deal with the general subject of removal of hydrogen fluoride from halogenated hydrocarbons. In particular, U.S. Pat. No. 4,128,626 discloses a method in which small amounts of hydrogen fluoride in a gas also containing hydrogen chloride are separated by contact with solid calcium chloride. It is indicated that this process has an application to the off gases from the fluorination of chlorinated hydrocarbons which is the general subject of the present invention.
Another approach is shown in U.S. Pat. No. 3,976,447 in which similar streams are scrubbed of their hydrogen fluoride content by contacting with a solid alkaline earth metal fluoride which has been prepared by fluorination of anhydrous calcium chloride. Such material is said to be regenerable and to have a high capacity for hydrogen fluoride.
Another method which employs a liquid rather than a solid absorbent is shown in U.S. Pat. No. 4,102,981 where hydrogen chloride is removed from halogenated hydrocarbons by scrubbing with an aqueous solution of trisodium phosphate and sodium hydroxide.
A substantially different technique is disclosed in U.S. Pat. No. 3,947,558 in which a liquid phase process for recovery of halogenated hydrocarbons employs a glycol to separate hydrogen fluoride from a liquid phase containing the desired halogenated hydrocarbons. In such a process it is anticipated that hydrogen chloride, which is a byproduct of the process for producing fluorinated hydrocarbons, will be separated first before the organic liquid phase is treated with a glycol to remove hydrogen fluoride.
It would be most desirable to find a method for purification of fluorinated hydrocarbons which would directly remove only the hydrochloric acid and hydrofluoric acid with essentially no loss of the valuable product, thus maximizing the yield while minimizing the waste which must be disposed of. If the acids could be recovered, then they could be sold or reused, again reducing to the waste disposal problems. The inventor has found a method for closely achieving these objectives.